Bi-directional seal assembly

ABSTRACT

A bi-directional seal assembly for sealing the annulus between an inner tubular member and an outer tubular member comprises an annular seal which in cross section includes a generally U-shaped first portion having a radially inner first leg and a radially outer second leg and a generally U-shaped second portion having a radially inner third leg and a radially outer fourth leg. The second and third legs are joined together such that the first leg engages the inner tubular member and the fourth leg engages the outer tubular member. Pressure below the seal urges the first leg into sealing engagement with the inner tubular member and forces the second and third legs radially outwardly to thereby urge the fourth leg into sealing engagement with the outer tubular member. Also, pressure above the seal urges the fourth leg into sealing engagement with the outer tubular member and forces the second and third legs radially inwardly to thereby urge the first leg into sealing engagement with the inner tubular member.

This application is a continuation of U.S. patent application Ser. No.12/661,712 filed on Mar. 22, 2010.

BACKGROUND OF THE INVENTION

The present invention is directed to a bi-directional seal assembly forsealing the annulus between an inner tubular member and an outer tubularmember. In particular, the invention is directed to a seal assemblywhich includes an annular metal seal that in cross section comprises twogenerally U-shaped portions which enable the seal to be pressureenergized from both above and below the seal assembly. The seal can beinstalled as an interference fit between the tubular members ormechanically energized into sealing engagement with the tubular membersafter it is installed.

Packoffs are commonly used in hydrocarbon production wells to seal theannulus between a wellhead and, e.g., a casing hanger which is landed inthe wellhead. These prior art packoffs often include one or more metalseals which are supported on a packoff body that is locked in placebetween the casing hanger and the wellhead. Either during or afterinstallation of the packoff, the seals are either mechanically orpressure energized into sealing engagement with both the wellhead andthe casing hanger.

Many prior art packoffs have only one metal seal and areuni-directional, that is, they are designed to seal in only onedirection. This poses difficulties when it is desired to pressure testthe packoff from a port external to the wellhead. Some packoffs includeelastomer seals for purposes of pressure testing. However, over time theelastomer can fail and the ability to test the packoff is consequentlylost.

Therefore, a need exists for a packoff seal which is bi-directional,that is, which is capable of sealing from both above and below. Inaddition, a need exists for a bi-directional packoff seal whose pressurereliability in both directions can be proved by pressure testing thepackoff from only one direction.

SUMMARY OF THE INVENTION

In accordance with the present invention, a bi-directional seal assemblyis provided for sealing between an inner tubular member and an outertubular member. The seal assembly comprises an annular seal which ispositioned in the annulus and which in cross section includes agenerally U-shaped first portion which comprises a radially inner firstleg and a radially outer second leg, the first and second legs defininga first cavity; and a generally U-shaped second portion which comprisesa radially inner third leg and a radially outer fourth leg, the thirdand fourth legs defining a second cavity. The second and third legs arejoined together between the first and fourth legs. Also, the first legengages the inner tubular member and the fourth leg engages the outertubular member to thereby sealingly divide the annulus into first andsecond parts.

In accordance with one embodiment of the invention, the second and thirdlegs are joined together such that the first cavity faces the first partof the annulus and the second cavity faces the second part of theannulus. In this embodiment, the seal assembly may also comprise a firstsupport ring which is positioned in the first cavity and a secondsupport ring which is positioned in the second cavity. The first supportring causes the first leg to remain engaged with the inner tubularmember under the influence of pressure in the second part of the annulusand the second support ring causes the fourth leg to remain engaged withthe outer tubular member under the influence of pressure in the firstpart of the annulus. Also, pressure in the first part of the annulusurges the first leg into sealing engagement with the inner tubularmember and forces the second leg radially outwardly to thereby urge thefourth leg into sealing engagement with the outer tubular member. Inaddition, pressure in the second part of the annulus urges the fourthleg into sealing engagement with the outer tubular member and forces thethird leg radially inwardly to thereby urge the first leg into sealingengagement with the inner tubular member.

In accordance with another embodiment of the invention, when the seal isin a relaxed condition the first support ring forms an interference fitwith the first cavity such that, when the first support ring is insertedinto the first cavity, the first support ring will urge the first leginto sealing engagement with the inner tubular member. In addition, whenthe seal is in relaxed condition the second support ring forms aninterference fit with the second cavity such that, when the secondsupport ring is inserted into the second cavity, the second support ringwill urge the fourth leg into sealing engagement with the outer tubularmember.

In accordance with yet another embodiment of the invention, the secondand third legs are joined together such that both the first and secondcavities face the first part of the annulus and the second and thirdlegs define a third cavity which faces the second part of the annulus.In this embodiment, the seal assembly may also comprise a first supportring which is positioned in the first cavity and a second support ringwhich is positioned in the second cavity. The first support ring causesthe first leg to remain engaged with the inner tubular member under theinfluence of pressure in the second part of the annulus and the secondsupport ring causes the fourth leg to remain engaged with the outertubular member under the influence of pressure in the second part of theannulus. Also, pressure in the second part of the annulus forces thesecond leg radially inwardly to thereby urge the first leg into sealingengagement with the inner tubular member and forces the third legradially outwardly to thereby urge the fourth leg into sealingengagement with the outer tubular member.

In accordance with yet another embodiment of the invention, the sealassembly further comprises a third support ring which is positioned inthe third cavity. The third support ring causes the first and fourthlegs to remain engaged with the inner and outer tubular members,respectively, under the influence of pressure in the first part of theannulus.

In accordance with a further embodiment of the invention, when the sealis in a relaxed condition the third support ring forms an interferencefit with the third cavity such that, when the third support ring isinserted into the third cavity, the third support ring will force thesecond and third legs toward the inner and outer tubular members,respectively, to thereby urge the first and fourth legs into sealingengagement with the inner and outer tubular members, respectively.

The present invention is also directed to a packoff which is positionedin an annulus between a wellhead and a tubular hanger which is landed inthe wellhead. The packoff comprises an upper packoff body; a first sealwhich is positioned below the upper packoff body; and a lower packoffbody which is positioned below the first seal and which is supported onone of the tubular hanger or the wellhead. In cross section, the firstseal includes a generally U-shaped first portion which comprises aradially inner first leg and a radially outer second leg, the first andsecond legs defining a first cavity; and a generally U-shaped secondportion which comprises a radially inner third leg and a radially outerfourth leg, the third and fourth legs defining a second cavity. Thesecond and third legs are joined together between the first and fourthlegs. Also, the first leg engages the tubular hanger and the fourth legengages the wellhead to thereby sealingly divide the annulus into afirst part located above the first seal and a second part located belowthe first seal.

In accordance with another embodiment of the packoff of the presentinvention, the second and third legs are joined together such that thefirst cavity faces the first part of the annulus and the second cavityfaces the second part of the annulus. In addition, the packoff maycomprise a first support ring which is positioned in the first cavityand a second support ring which is positioned in the second cavity. Thefirst support ring causes the first leg to remain engaged with thetubular hanger under the influence of pressure in the second part of theannulus and the second support ring causes the fourth leg to remainengaged with the wellhead under the influence of pressure in the firstpart of the annulus. Also, pressure in the first part of the annulusurges the first leg into sealing engagement with the tubular hanger andforces the second leg radially outwardly to thereby urge the fourth leginto sealing engagement with the wellhead. In addition, pressure in thesecond part of the annulus urges the fourth leg into sealing engagementwith the wellhead and forces the third leg radially inwardly to therebyurge the first leg into sealing engagement with the tubular hanger.

In accordance with yet another embodiment of the packoff of the presentinvention, when the first seal is in a relaxed condition the firstsupport ring forms an interference fit with the first cavity such that,when the first support ring is inserted into the first cavity, the firstsupport ring will urge the first leg into sealing engagement with thetubular hanger. In addition, when the first seal is in a relaxedcondition the second support ring forms an interference fit with thesecond cavity such that, when the second support ring is inserted intothe second cavity, the second support ring will urge the fourth leg intosealing engagement with the wellhead.

In accordance with still another embodiment of the packoff of thepresent invention, the packoff also comprises a second seal which ispositioned between the first seal and the lower packoff body and whichin cross section comprises a generally U-shaped third portion whichcomprises a radially inner fifth leg and a radially outer sixth leg, thefifth and sixth legs defining a third cavity; and a generally U-shapedfourth portion which comprises a radially inner seventh leg and aradially outer eighth leg, the seventh and eighth legs defining a fourthcavity. The sixth and seventh legs are joined together between the fifthand eighth legs. Also, the fifth leg engages the tubular hanger and theeighth leg engages the wellhead to thereby seal the annulus.

Thus, the present invention provides a bi-directional seal assemblywhich effectively seals from both above and below. Consequently,additional seals do not need to be employed in conjunction with the sealassembly. In addition, pressure testing of the seal assembly from onedirection will establish that the seal assembly is cable of effectivelysealing from both directions.

These and other objects and advantages of the present invention will bemade apparent from the following detailed description, with reference tothe accompanying drawings. In the drawings, the same reference numbersmay be used to denote similar components in the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional representation of one embodiment of the sealassembly of the present invention showing the seal component of theinvention prior to being energized by an exemplary support ring;

FIG. 2 is a cross sectional representation of the seal component shownin FIG. 1;

FIG. 3 is a cross sectional representation of the seal assembly of FIG.1 showing the seal component after being energized by the support ring;

FIG. 4 is a cross sectional representation of a second embodiment of theseal assembly of the present invention;

FIG. 5 is a cross sectional representation of a third embodiment of theseal assembly of the present invention;

FIG. 6 is a cross sectional representation of a fourth embodiment of theseal assembly of the present invention showing the seal component of theinvention prior to being energized by another exemplary support ring;

FIG. 7 is a cross sectional representation of the seal component shownin FIG. 6;

FIG. 8 is a cross sectional representation of an embodiment of the sealassembly of the present invention being used as an annulus packoff;

FIG. 9 is a cross sectional representation of a second embodiment of theseal assembly of the present invention shown being used as an annuluspackoff;

FIG. 10 is a cross sectional representation of a third embodiment of theseal assembly of the present invention shown being used as an annuluspackoff;

FIG. 11 is a cross sectional representation of a fourth embodiment ofthe seal assembly of the present invention shown being used as anannulus packoff; and

FIG. 12 is a cross sectional representation of a fifth embodiment of theseal assembly of the present invention shown being used as an annuluspackoff.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 2, one embodiment of the seal assembly of thepresent invention, which is indicated generally by reference number 10,is shown positioned in the annulus between an inner tubular member 12and an outer tubular member 14. The inner and outer tubular members 12,14 may comprise any type of fluid handling pipes or conduits. Whenengaged between the inner and outer tubular members 12, 14, the sealassembly 10 sealingly divides the annulus into a first part 16 locatedbelow the seal assembly and a second part 18 located above the sealassembly.

The seal assembly 10 includes an annular metal seal 20 which in crosssection includes a radially inner, generally U-shaped first portion 22and a radially outer, generally U-shaped second portion 24. The firstportion 22 comprises a radially inner first leg 26 and a radially outersecond leg 28 which together define a first cavity 30. Similarly, thesecond portion 24 comprises a radially inner third leg 32 and a radiallyouter fourth leg 34 which together define a second cavity 36. Whenpositioned in the annulus, the first leg 26 engages the inner tubularmember 12 and the fourth leg 34 engages the outer tubular member 14. Theseal 20 may be installed as an interference fit between the inner andouter tubular members 12, 14 or mechanically energized into engagementwith the inner and outer tubular members by a separate member.

In the embodiment of the invention shown in FIGS. 1 and 2, the first andsecond portions 22, 24 are oriented in opposite directions and thesecond and third legs 28, 32 are joined together at a point 38 which islocated radially between the first and fourth legs 26, 34. In thisorientation, the first cavity 30 faces the first part 16 of the annulusand the second cavity 36 faces the second part 18 of the annulus.

Referring also to FIG. 3, the seal assembly 10 may also comprise firstand second support rings 40, 42 to help support the seal 20 within theannulus and to facilitate either the mechanical or pressure energizationof the first and fourth legs 26, 34. In the embodiment of the inventionshown in FIGS. 1 and 3, for example, the first and second support rings40, 42 are used to mechanically energize the first and fourth legs 26,34 into sealing engagement with the inner and outer tubular members 12,14. In these figures, the first support ring 40 is shown in phantom forpurposes of clarity.

For the purpose of mechanically energizing the first and fourth legs 26,34, the first support ring 40 and preferably also the seal 20 aresupported on a seat ring 44 which in turn is supported on one of theinner or outer tubular members 12, 14. Also, each support ring 40, 42ideally comprises a cross section which is configured to form aninterference fit with its corresponding cavity 30, 36 when the seal 20is in its relaxed or un-energized state. Thus, when the second supportring 42 is forced down against the seal 20 by, e.g., an energizingmandrel 46, the first support ring 40 will enter the first cavity 30 andforce the first leg 26 radially inwardly into sealing engagement withthe inner tubular member 12, and the second support ring 42 will enterthe second cavity 36 and force the fourth leg 34 radially outwardly intosealing engagement with the outer tubular member 14.

In an alternative embodiment of the invention, the first and fourth legs26, 34 are pressure-energized into sealing engagement with the inner andouter tubular members 12, 14. In this embodiment, pressure in the firstpart 16 of the annulus, which is represented by the many small arrows inFIG. 3, will urge the first leg 26 into sealing engagement with theinner tubular member 12 and force the second and third legs 28, 32radially outwardly to thereby urge the fourth leg 34 into sealingengagement with the outer tubular member 14. Similarly, pressure in thesecond part 18 of the annulus will urge the fourth leg 34 into sealingengagement with the outer tubular member 14 and bias the second andthird legs 28, 32 radially inwardly to thereby urge the first leg 26into sealing engagement with the inner tubular member.

Although not required, the first and second support rings 40, 42 may beused to facilitate the pressure energization of the first and fourthlegs 26, 34. As shown in FIG. 3, pressure in the first part 16 of theannulus, which is represented by the many small arrows, pushes radiallyinwardly on the fourth leg 34. However, because the second support ring42 occupies the second cavity 36, the forces resulting from the pressureacting on the third and fourth legs 32, 34 cancel each other out.Consequently, the only force acting on the fourth leg 34 results fromthe pressure acting on the second leg, and this force acts radiallyoutwardly to urge the fourth leg into sealing engagement with the outertubular member 14. The first support ring 40 plays a similar role inurging the first leg 26 into sealing engagement with the inner tubularmember 12 under the influence of pressure in the second part 18 of theannulus. In this embodiment, the support rings 40, 42 need not form aninterference fit with their respective cavities 30, 36.

Referring again to FIG. 2, the seal 20 may also comprise an innersealing bump 48 which is formed on the distal end of the first leg 26and an outer bump 50 which is formed on the distal end of the fourth leg34. The bumps 48, 50 serve to concentrate the sealing forces of thefirst and fourth legs 26, 34 against the inner and outer tubular members12, 14, which provides for a more effective seal between the seal 20 andthese members.

Referring to FIG. 4, another embodiment of the seal assembly of thepresent invention comprises an annular seal, generally 52, which incross section includes a radially inner, generally U-shaped firstportion 22 and a radially outer, generally U-shaped second portion 24.The first portion 22 comprises a radially inner first leg 26 and aradially outer second leg 28 which together define a first cavity 30.Similarly, the second portion 24 comprises a radially inner third leg 32and a radially outer fourth leg 34 which together define a second cavity36. The first and second portions 22, 24 are oriented in oppositedirections and the second and third legs 28, 32 are joined together at apoint 38 which is located radially between the first and fourth legs 26,34.

In this embodiment, the first portion 22 comprises a generally flatfirst apex 54 which extends radially between approximately the inneredge of the first leg 26 and the outer edge of the second leg 28.Likewise, the second portion 24 comprises a generally flat second apex56 which extends radially between approximately the inner edge of thethird leg 32 and the outer edge of the fourth leg 34. The first andfourth legs 26, 34 are oriented generally axially, and the distal end ofthe first leg is generally aligned with the second apex 56 while thedistal end of the fourth leg is generally aligned with the first apex54.

The seal 52 may be installed as an interference fit between the innerand outer tubular members and does not require support rings to aid inits mechanical or pressure energization. In addition, the seal 52 maycomprise an inner sealing bump 48 which is formed on the first leg 26and an outer sealing bump 50 which is formed on the fourth leg 34.

A further embodiment of the seal assembly of the present invention isshown in FIG. 5. The seal assembly of this embodiment is comprised of annon-metallic seal, generally 58, which is positioned between upper andlower endcaps 60, 62 that are made of a material which is more rigidthan the seal material. As in the previous embodiments, the seal 58includes a radially inner, generally U-shaped first portion 22 and aradially outer, generally U-shaped second portion 24. The first portion22 comprises a radially inner first leg 26 and a radially outer secondleg 28 which together define a first cavity 30. Similarly, the secondportion 24 comprises a radially inner third leg 32 and a radially outerfourth leg 34 which together define a second cavity 36. The first andsecond portions 22, 24 are oriented in opposite directions and thesecond and third legs 28, 32 are joined together at a point 38 which islocated radially between the first and fourth legs 26, 34.

The upper and lower endcaps 60, 62 are configured to conform to theshape of the seal 58. In addition, the first leg 26 comprises a radiallyinner sealing face 64 which is located between the radially inner endsof the upper and lower endcaps, and the fourth leg 34 comprises aradially outer sealing face 66 which is located between the radiallyouter ends of the upper and lower endcaps. As with the seal 52, the seal58 may be installed as an interference fit between the inner and outertubular members and does not require support rings to aid in itsmechanical or pressure energization.

Another embodiment of the seal assembly of the present invention isshown in FIGS. 6 and 7. The seal assembly of this embodiment, generally100, comprises an annular seal 102 which in cross section includes aradially inner, generally U-shaped first portion 104, a radiallyintermediate, generally U-shaped second portion 106 and a radiallyouter, generally U-shaped third portion 108. The first portion 104comprises a radially inner first leg 110 and a radially outer second leg112 which together define a first cavity 114. Similarly, the secondportion 106 comprises a radially inner third leg 116 and a radiallyouter fourth leg 118 which together define a second cavity 120, and thethird portion 108 comprises a radially inner fifth leg 122 and aradially outer sixth leg 124 which together define a third cavity 126.When the seal 102 is positioned in the annulus between the inner andouter tubular members 12, 14, the first leg 110 engages the innertubular member and the sixth leg 124 engages the outer tubular member.As with the seal 20, the seal 102 may be installed as an interferencefit between the inner and outer tubular members 12, 14 or mechanicallyenergized into engagement with the inner and outer tubular members by aseparate member.

In this embodiment of the invention, the first and second portions 104,106 are oriented in opposite directions and the second and thirdportions 106, 108 are oriented in opposite directions. In thisorientation, both the first and third cavities 114, 126 face the firstpart 16 of the annulus and the second cavity 120 faces the second part18 of the annulus.

As with the seal assembly 10, the seal assembly 100 may comprise anumber of optional support rings to help support the seal 102 within theannulus and to facilitate either the mechanical or pressure energizationof the first and sixth legs 110, 124 into sealing engagement with theinner and outer tubular members 12, 14. For instance, a first supportring 128 may be positioned in the first cavity 114, a second supportring 130 may be positioned in the second cavity 120 and a third supportring 132 may be positioned in the third cavity 126.

In the embodiment of the invention shown in FIG. 6, the second supportring 130 is used to mechanically energize the first and sixth legs 110,124 into sealing engagement with the inner and outer tubular members 12,14. In this embodiment, the seal 102 is supported on a seat ring 134which in turn is supported on one of the inner or outer tubular members12, 14. Also, the second support ring 130 comprises a cross sectionwhich is configured to form an interference fit with the third cavity120 when the seal 102 is in its relaxed or un-energized condition. Thus,when the second support ring 130 is forced down against the seal 102 by,e.g., an energizing mandrel 136, the third support ring 130 will enterthe second cavity 120 and force the second leg 112 radially inwardly andthe fifth leg 122 radially outwardly to thereby urge the first leg 110into sealing engagement with the inner tubular member 12 and the sixthleg 124 into sealing engagement with the outer tubular member 14.

In this embodiment, the first and third support rings 128, 132 may beused to maintain the proper spacing between the first and second legs110, 112 and between the fifth and sixth legs 122, 124, respectively.Alternatively, the first and third support rings 128, 132 may be used tomechanically energize the first and sixth legs 110, 124, in which eventthe first and third supports rings are configured to form aninterference fit with their respective cavities 114, 126 and the secondsupport ring 130 is optionally used to maintain the proper spacingbetween the second and fifth legs 112, 122. Alternatively, all threesupport rings may be used to mechanically energize the first and sixthlegs 110, 124, in which event the support rings would be designed toform an interference fit with their respective cavities.

In an alternative embodiment of the invention, the first and sixth legs110, 124 are pressure-energized into sealing engagement with the innerand outer tubular members 12, 14. In this example, pressure in the firstpart 16 of the annulus will urge the first and sixth legs 110, 124 intosealing engagement with the inner and outer tubular members 12, 14.Also, pressure in the second part 18 of the annulus will force thesecond leg 112 radially inwardly and the fifth leg 122 radiallyoutwardly to thereby urge the first and sixth legs 110, 124 into sealingengagement with the inner and outer tubular members 12, 14.

Although not required, the first and third support rings 128, 132 may beused to facilitate the pressure energization of the first and sixth legs110, 124. In this regard, pressure in the second part 18 of the annuluspushes radially outwardly on the first leg 110 and radially inwardly onthe sixth leg 124. However, the first support ring 128 will cause theresultant forces acting on the first and second legs 110, 112 to canceleach other out. Similarly, the third support ring 132 will cause theresultant forces acting on the fifth and sixth legs 122, 124 to canceleach other out. As a result, the only forces acting on the first andsixth legs 110, 124 will be those resulting from the pressure acting onthe third and fourth legs 116, 118, and these forces will urge the firstand sixth legs into sealing engagement with the inner and outer tubularmembers 12, 14.

The second support ring 130 may also be used to facilitate the pressureenergization of the first and sixth legs 110, 124. In this regard, thesecond support ring 130 may be positioned in the second cavity 120 toprevent pressure in the first part 16 of the annulus from pushing thethird and fourth legs 116, 118 together and consequently pulling thefirst and sixth legs 110, 124 out of engagement with the inner and outertubular members 12, 14. In this embodiment, the support rings 128, 130,132 need not form an interference fit with their respective cavities114, 120, 126.

Another embodiment of the seal assembly of the present invention isshown in FIG. 8. The seal assembly of this embodiment is configured as apackoff, generally 200, which by way of example is shown installed inthe annulus between a typical wellhead 204 and a representative tubularhanger 202, such as a tubing or casing hanger. The packoff 200 includesa pair of upper and lower seal assemblies 206, 208 which are positionedbetween an upper packoff body 210 and a lower packoff body 212, thelatter of which is supported on an annular seat 214 that is formed onthe outer diameter surface of the tubular hanger 202.

Each seal assembly 206, 208 is similar to the seal assembly 10 describedabove. Thus, each seal assembly 206, 208 includes an annular seal 216,218 which comprises the general cross sectional configuration of theseal 20. Accordingly, the same reference numbers which were used todescribe the seal 20 will be used to describe seals 216, 218.

When the packoff 200 is installed in the annulus between the wellhead204 and the tubular hanger 202, the first legs 26 of the upper and lowerseals 216, 218 will sealingly engage the tubular hanger and the fourthlegs 34 of the upper and lower seals will sealingly engage the wellhead204. In addition, the upper seal 216 is oriented such that the firstcavity 30 between the first and second legs 26, 28 faces upward and thesecond cavity 36 between the third and fourth legs 32, 34 facesdownward. Also, the lower seal 218 is oriented such that the firstcavity 30 between the first and second legs 26, 28 faces downward andthe second cavity 36 between the third and fourth legs 32, 34 facesupward.

The upper and lower seal assemblies 206, 208, the upper packoff body 210and the lower packoff body 212 are preferably secured together bysuitable means. In the embodiment of the invention shown in FIG. 8, forexample, the upper seal 216 includes a first flange 220 which extendsdownwardly from the apex of the first generally U-shaped portion 22 anda second flange 222 which extends upwardly from the apex of the secondgenerally U-shaped portion 24. Similarly, the lower seal 218 includes athird flange 224 which extends upwardly from the first U-shaped portion22 and a fourth flange 226 which extends downwardly from the apex of thesecond U-shaped portion 24. The second flange 222 is connected to theupper packoff body 210 by a first retainer strip 228, the fourth flange226 is connected to the lower packoff body 212 by a second retainerstrip 230, and the first and third flanges 220, 224 are connectedtogether by a third retainer strip 232.

The upper and lower packoff bodies 210, 212 may be recessed respectivelyat 234 and 236 to accommodate the flanges 222 and 226, and the flangesand the packoff bodies are mutually grooved to accommodate the retainerstrips 228, 230, 232. In addition, the groove in one of the flanges 220,224 is ideally elongated in the axial direction to allow the upper andlower seals 216 and 218 to displace toward each other during setting ofthe packoff 200.

Each of the upper and lower seal assemblies 206, 208 may also includefirst and second support rings 40, 42 which are positioned in the firstand second cavities 30, 36, respectively. In this regard, the upperpackoff body 210 ideally includes a lower shoulder portion 238 whichengages the first support ring 40 of the upper seal assembly 206, andthe lower packoff body 212 ideally includes an upper seat portion 240which engages the first support ring 40 of the lower seal assembly 208.In addition, the packoff 200 preferably includes a spacer ring 242 whichis positioned between the second support ring 42 of the upper sealassembly 206 and the second support ring 42 of the lower seal assembly208. The spacer ring 242 may include an annular lip 244 which is engagedby the bottom of the first flange 220 of the upper seal assembly 206during setting of the packoff 200.

In use, the packoff 200 is installed using an appropriate tool and islocked into place in the annulus using a convention lockdown mechanismconnected to the upper packoff body 210. Once installed and optionallyenergized, the seal assemblies 206, 208 will function in a mannersimilar to the seal assembly 10 to provide a bi-directional seal againstpressure acting from above the packoff 200 and pressure acting frombelow the packoff. In addition, the seal assemblies 206, 208 willcontain the pressure introduced through a test port 246 in the wellhead204 during pressure testing of the packoff 200.

A second embodiment of a packoff which is based on the seal assembly ofthe present invention is shown in FIG. 9. The packoff of thisembodiment, generally 300, includes an upper annular seal 216 which isnested within a lower annular seal 218. In other words, the firstportion 22 of the lower seal 218 is positioned at least partially withinthe first cavity 30 of the upper seal 216 and the second portion 24 ofthe upper seal is positioned at least partially within the second cavity36 of the lower seal. In addition, the first portion 22 of the lowerseal 218 is preferably configured to form a sliding fit with the firstcavity 30 of the upper seal 216, and the second portion 24 of the upperseal is preferably configured to form a sliding fit with the secondcavity 36 of the lower seal.

The lower seal 218 is supported on a rawer packoff body or seat ring 212which in turn is supported on the tubular hanger 202. The seat ring 212includes an upper flange 302 which is preferably configured to form asliding fit with the first cavity 30 of the lower seal. The lower seal218 includes an integral support ring 304 which is connected to the seatring 212 through a cam and groove arrangement 306. In addition, theupper seal 216 is connected to the lower seal 218 through a cam andgroove arrangement 308.

During installation of the packoff 300, the seat ring 212 and the upperand lower seals 216, 218 are assembled and lowered as a unit into theannulus between the tubular hanger 202 and the wellhead 204. This actionmay be facilitated by the use of a suitable tool (not shown) whichengages a setting mandrel 310 that is connected to or formed integrallywith the upper seal 216. An upper packoff body or energizing mandrel 312which is configured to form an interference fit with the second cavity36 of the upper seal 216 is then forced down into the second cavity.This action forces the first legs 26 of the first and second seals 216,218 into sealing engagement with the tubular hanger 202 and the fourthlegs 34 of the first and second seals into sealing engagement with thewellhead 204 to thereby seal the annulus.

Another embodiment of a packoff which is based on the seal assembly ofthe present invention is shown in FIG. 10. The packoff of thisembodiment, generally 400, is similar to the packoff 300 describedabove. In this embodiment, however, the first portion 22 of the lowerseal 218 is preferably configured to form an interference fit with thefirst cavity 30 of the upper seal 216, and the second portion 24 of theupper seal is preferably configured to form an interference fit with thesecond cavity 36 of the lower seal. In addition, the upper seal 216 isconnected to an upper packoff body or energizing mandrel 402 through acam and groove arrangement 404 and to the lower seal 218 through a camand groove arrangement 406. The lower seal 218 in turn is connected to alower packoff body or seat ring 212 through a cam and groove arrangement408.

During installation of the packoff 400, the assembly of the seat ring212, the lower seal 218, the upper seal 216 and the energizing mandrel402 is lowered into the annulus between the tubular hanger 202 and thewellhead 204 until the seat ring comes to rest on a seat 410 which isformed on the outer surface of the tubular hanger. The energizingmandrel 402 is then forced down against the upper seal 216. This actionforces the second portion 24 of the upper seal 216 into the secondcavity 36 of the lower seal 218, which in turn forces the first andfourth legs 26, 34 of the lower seal into sealing engagement with thetubular hanger 202 and the wellhead 204, respectively. Further downwardmovement of the energizing mandrel 402 forces the energizing mandrelinto the second cavity 36 of the upper seal 216, which in turn forcesthe first and fourth legs of the upper seal into sealing engagement withthe tubular hanger 202 and the wellhead 204, respectively.

Yet another embodiment of a packoff which incorporates the seal assemblyof the present invention is shown in FIG. 11. The packoff of thisembodiment, generally 500, illustrates a particular feature of thepresent invention, namely, that the first and second generally U-shapedportions of the annular seal do not need to be formed integrally orconnected together.

As shown in FIG. 11, the packoff 500 includes an upper seal 502 and alower seal 502′. The upper seal 502 includes a radially inner, generallyU-shaped first portion 22 and a radially outer, generally U-shapedsecond portion 24. The first portion 22 comprises part of an upperpackoff body or energizing mandrel 504 while the second portion 24comprises a distinct seal ring. As in the previous embodiments, thefirst portion 22 includes a radially inner first leg 26 and a radiallyouter second leg 28 which together define a first cavity 30, and thesecond portion 24 comprises a radially inner third leg 32 and a radiallyouter fourth leg 34 which together define a second cavity 36. However,the second and third legs 28, 32 are not joined together. Rather, thesecond and third legs 28, 32 are positioned side by side and are sealedagainst each other at a point which is located radially between thefirst and fourth legs 26, 34.

The second portion 24 is ideally configured to form an interference fitbetween the first portion 22 and the wellhead 204 after the packoff 500is set. In addition, the second portion 24 may comprise radially innerand outer seal bumps 48, 50 which are formed on the third and fourthlegs 32, 34, respectively. Thus, after the packoff 500 is set the secondand third legs 28, 32 will be sealed against each other at the innerseal bump 48.

Similar to the upper seal 502, the lower seal 502′ includes a radiallyinner, generally U-shaped first portion 22′ and a radially outer,generally U-shaped second portion 24′. The first portion 22′ comprises apart of the upper packoff body 504 located below the first portion 22,while the second portion 24′ comprises a distinct seal ring. The firstportion 22′ includes a radially inner first leg 26′ and a radially outersecond leg 28′ which together define a first cavity 30′, and the secondportion 24′ comprises a radially inner third leg 32′ and a radiallyouter fourth leg 34′ which together define a second cavity 36′. Thesecond and third legs 28′, 32′ are positioned side by side and aresealed against each other at a point which is located radially betweenthe first and fourth legs 26′, 34′.

As with the second portion 24 of the upper seal 502, the second portion24′ of the lower seal 502′ is ideally configured to form an interferencefit between the first portion 22′ and the wellhead 204 after the packoff500 is set. In addition, the second portion 22′ may comprise radiallyinner and outer seal bumps 48′, 50′ which are formed on the third andfourth legs 32′, 34′, respectively. In this manner, after the packoff500 is set the second and third legs 28′, 32′ will be sealed againsteach other at the inner seal bump 48′.

The lower seal 502′ is supported on a lower packoff body or seat ring506 which in turn is supported on the tubular hanger 202 or the wellhead204. Furthermore, the upper packoff body 504 includes an annular hookring 508 which depends downwardly from the second leg 28′ of the lowerseal 502′ and which, prior to installation of the packoff 500, engages astop ring 510 on the lower packoff body 506 to thereby link the upperpackoff body to the lower packoff body.

During installation of the packoff 500, the assembly of the upperpackoff body 504, the upper and lower seals 502, 502′ and the lowerpackoff body 506 is lowered and landed in the annulus between thetubular hanger 202 and the wellhead 204. The upper packoff body 504 isthen forced downward until it lands on the second portion 24 of theupper packoff body. This action energizes the packoff 500 into sealingengagement with the tubular hanger 202 and the wellhead 204. Inparticular, as the first portion 22 of the upper seal 502 moves to aposition adjacent the second portion 24 of the upper seal, the first leg26 is urged into sealing engagement with the tubular hanger 202, thefourth leg 34 is urged into sealing engagement with the wellhead 204 andthe second and third legs 28, 32 are urged into sealing engagementagainst each other. Similarly, as the as the first portion 22′ of thelower seal 502′ moves to a position adjacent the second portion 24′ ofthe lower seal, the first leg 26′ is urged into sealing engagement withthe tubular hanger 202, the fourth leg 34′ is urged into sealingengagement with the wellhead 204 and the second and third legs 28′, 32′are urged into sealing engagement against each other.

Another embodiment of a packoff which incorporates the seal assembly ofthe present invention is shown in FIG. 12. The packoff of thisembodiment, generally 600, is similar to the packoff 500 describedabove. However, in the packoff 600 the upper seal 502 comprises a thirdgenerally U-shaped portion 602 which is located radially inwardly of thefirst portion 22 and the lower seal 502′ comprises a third generallyU-shaped portion 602′ which is located radially inwardly of the firstportion 22′. As with the packoff 500, the third portions 602, 602′comprise distinct seal rings.

The third portion 602 of the upper seal 502 forms an interference fitbetween the first portion 22 and the tubular hanger 202 when the packoff600 is set. Similarly, the third portion 602′ of the lower seal 502′forms an interference fit between the first portion 22′ and the tubularhanger 202 when the packoff 600 is set. Thus, when the upper packoffbody or energizing mandrel 502 is moved downward toward the lowerpackoff body or seat 506, the upper and lower seals 502, 502′ will beenergized into sealing engagement with the tubular hanger 202 and thewellhead 204.

It should be recognized that, while the present invention has beendescribed in relation to the preferred embodiments thereof, thoseskilled in the art may develop a wide variation of structural andoperational details without departing from the principles of theinvention. For example, the various elements shown in the differentembodiments may be combined in a manner not illustrated above.Therefore, the appended claims are to be construed to cover allequivalents falling within the true scope and spirit of the invention.

What is claimed is:
 1. A seal assembly for sealing an annulus betweenconcentric inner and outer tubular members, the seal assemblycomprising: an annular first seal which is positioned between the innerand outer tubular members to thereby divide the annulus into axiallyspaced first and second parts, the first seal in cross sectioncomprising: a generally U-shaped first seal portion which comprises aradially inner first leg, a radially outer second leg, and a firstcavity that is located between the first and second legs, the first legbeing configured to sealingly engage the inner tubular member; agenerally U-shaped second seal portion which is located radiallyoutwardly of the first seal portion and which comprises a radially innerthird leg, a radially outer fourth leg, and a second cavity that islocated between the third and fourth legs, the fourth leg beingconfigured to sealingly engage the outer tubular member; wherein thefirst and second seal portions are oriented generally parallel to anaxial centerline of the tubular members and the second and third legsare joined at a position located radially between the first and fourthlegs such that the first cavity faces the first part of the annulus andthe second cavity faces the second part of the annulus, the second andthird legs being joined such that movement of the second leg radiallyoutwardly forces the third leg radially outwardly and movement of thethird leg radially inwardly forces the second leg radially inwardly; afirst support ring which is positioned in the first cavity and isconfigured to maintain a minimum radial distance between the first andsecond legs; and a second support ring which is positioned in the secondcavity and is configured to maintain a minimum radial distance betweenthe third and fourth legs; wherein a pressure in the first part of theannulus greater than a pressure in the second part of the annulus forcesthe first and second legs radially apart, while the second support ringmaintains the minimum radial distance between the third and fourth legs,to thereby maintain the first leg in sealing engagement with the innertubular member and the fourth leg in sealing engagement with the outertubular member; and wherein a pressure in the second part of the annulusgreater than a pressure in the first part of the annulus forces thethird and fourth legs radially apart, while the first support ringmaintains the minimum radial distance between the first and second legs,to thereby maintain the first leg in sealing engagement with the innertubular member and the fourth leg in sealing engagement with the outertubular member; whereby the first and second legs maintain sealingengagement with the inner and outer tubular members, respectively,whether the pressure in the first part of the annulus is greater thanthe pressure in the second part of the annulus or the pressure in thesecond part of the annulus is greater than the pressure in the firstpart of the annulus.
 2. The seal assembly of claim 1, wherein the firstleg sealingly engages the inner tubular member through at least a firstsealing bump which is formed on a radially inner surface of the firstleg and the fourth leg sealingly engages the outer tubular memberthrough at least a second sealing bump which is formed on a radiallyouter surface of the fourth leg.
 3. The seal assembly of claim 2,wherein the first and second sealing bumps are located approximately ina first plane which is perpendicular to the axial centerline of theinner and outer tubular members, the first cavity comprises an axiallyinner end which is located approximately in a second plane that isparallel to the first plane and is spaced apart from the first plane ina direction toward the second part of the annulus, and the second cavitycomprises an axially inner end which is located approximately in a thirdplane that is parallel to the first plane and is spaced apart from thefirst plane in a direction toward the first part of the annulus.
 4. Theseal assembly of claim 1, wherein the first leg comprises a radiallyouter surface which defines a radially inner side of the first cavity,the fourth leg comprises a radially inner surface which defines aradially outer side of the second cavity, the first support ringcomprises a first portion which conforms to substantially the entireradially outer surface of the first leg, and the second support ringcomprises a first portion which conforms to substantially the entireradially inner surface of the fourth leg.
 5. The seal assembly of claim4, wherein the second leg comprises a radially inner surface whichdefines a radially outer side of the first cavity, the third legcomprises a radially outer surface which defines a radially inner sideof the second cavity, the first support ring comprises a second portionwhich conforms to substantially the entire radially inner surface of thesecond leg, and the second support ring comprises a second portion whichconforms to substantially the entire radially outer surface of the thirdleg.
 6. The seal assembly of claim 1, further comprising first andsecond packoff members between which the first seal is positioned, thefirst packoff member being supported on at least one of the inner andouter tubular members and the second packoff member being movable towardthe first packoff member to thereby cause the first and second supportrings to mechanically energize the first and fourth legs into sealingengagement with the inner and outer tubular members, respectively. 7.The seal assembly of claim 6, wherein the first support ring is formedintegrally with the first packoff member.
 8. The seal assembly of claim7, wherein the second support ring is formed integrally with the secondpackoff member.
 9. The seal assembly of claim 1, further comprising: anannular second seal which is positioned in the annulus axially adjacentthe first seal, the second seal in cross section comprising: a generallyU-shaped third seal portion which comprises a radially inner fifth leg,a radially outer sixth leg, and a third cavity that is located betweenthe fifth and sixth legs, the fifth leg being configured to sealinglyengage the inner tubular member; a generally U-shaped fourth sealportion which is located radially outwardly of the third seal portionand which comprises a radially inner seventh leg, a radially outereighth leg, and a fourth cavity that is located between the seventh andeighth legs, the eighth leg being configured to sealingly engage theouter tubular member; wherein the third and fourth seal portions areoriented generally parallel to the axial centerline of the tubularmembers and the sixth and seventh legs are joined at a position locatedradially between the fifth and eighth legs such that the third cavityfaces the first part of the annulus and the fourth cavity faces thesecond part of the annulus, the sixth and seventh legs being joined suchthat movement of the sixth leg radially outwardly forces the seventh legradially outwardly and movement of the seventh leg radially inwardlyforces the sixth leg radially inwardly; a third support ring which ispositioned in the third cavity and is configured to maintain a minimumradial distance between the fifth and sixth legs; and a fourth supportring which is positioned in the fourth cavity and is configured tomaintain a minimum radial distance between the seventh and eighth legs;10. The seal assembly of claim 9, further comprising first and secondpackoff members between which the first and second seals are positioned,the first packoff member being supported on at least one of the innerand outer tubular members and the second packoff member being movabletoward said first packoff member to thereby cause the first and secondsupport rings to mechanically energize the first and fourth legs intosealing engagement with the inner and outer tubular members,respectively, and the third and fourth support rings to mechanicallyenergize the fifth and eighth legs into sealing engagement with theinner and outer tubular members, respectively.
 11. The seal assembly ofclaim 10, wherein the first support ring is formed integrally with thefirst packoff member and the fourth support ring is formed integrallywith the second packoff member.
 12. The seal assembly of claim 11,wherein the second support ring is formed integrally with the fourthseal portion and the third support ring is formed integrally with thefirst seal portion.
 13. A seal assembly for sealing an annulus betweenconcentric inner and outer tubular members, the seal assembly comprisingan annular first seal which is positioned between the inner and outertubular members to thereby divide the annulus into axially spaced firstand second parts, the first seal in cross section comprising: agenerally U-shaped first seal portion which includes a radially innerfirst leg, a radially outer second leg, and a first cavity that islocated between the first and second legs, the first leg comprising afirst sealing bump which is configured to sealingly engage the innertubular member; a generally U-shaped second seal portion which islocated radially outwardly of the first seal portion and which includesa radially inner third leg, a radially outer fourth leg, and a secondcavity which is located between the third and fourth legs, the fourthleg comprising a second sealing bump which is configured to sealinglyengage the outer tubular member; wherein the first and second sealportions are oriented generally parallel to an axial centerline of thetubular members and the second and third legs are joined at a positionlocated radially between the first and fourth legs such that the firstcavity faces the first part of the annulus and the second cavity facesthe second part of the annulus, the second and third legs being joinedsuch that movement of the second leg radially outwardly forces the thirdleg radially outwardly and movement of the third leg radially inwardlyforces the second leg radially inwardly; wherein the first and secondsealing bumps are located approximately in a first plane which isperpendicular to the axial centerline of the inner and outer tubularmembers, the first cavity comprises an axially inner end which islocated approximately in a second plane that is parallel to the firstplane and is spaced apart from the first plane in a direction toward thesecond part of the annulus, and the second cavity comprises an axiallyinner end which is located approximately in a third plane that is spacedapart from the first plane in a direction toward the first part of theannulus.
 14. The seal assembly of claim 13, wherein a radially innersurface of the first leg and a radially outer surface of the fourth legextend generally parallel to the axial centerline of the inner and outertubular members.
 15. The seal assembly of claim 14 wherein the firstseal portion comprises a generally flat first apex which extendsgenerally perpendicularly between the radially inner surface of thefirst leg and a radially outer surface of the second leg, and whereinthe second seal portion comprises a generally flat second apex whichextends generally perpendicularly between the radially outer surface ofthe fourth leg and a radially inner surface of the third leg.
 16. A sealassembly for sealing an annulus between concentric inner and outertubular members, the seal assembly comprising: an annular first sealwhich is positioned in the annulus to thereby divide the annulus intoaxially spaced first and second parts, the first seal in cross sectioncomprising: a generally U-shaped first seal portion which comprises aradially inner first leg, a radially outer second leg, and a firstcavity that is located between the first and second legs, the first legbeing configured to sealingly engage the inner tubular member; agenerally U-shaped second seal portion which is located radiallyoutwardly of the first portion and which comprises a radially innerthird leg, a radially outer fourth leg, and a second cavity that islocated between the third and fourth legs, the fourth leg beingconfigured to sealingly engage the outer tubular member; wherein thefirst and second seal portions are separate members and the second andthird legs are sealingly engaged with each other such that the firstcavity faces the first part of the annulus and the second cavity facesthe second part of the annulus, the second and third legs beingconfigured such that that movement of the second leg radially outwardlyforces the third leg radially outwardly and movement of the third legradially inwardly forces the second leg radially inwardly: wherein apressure in the first part of the annulus greater than a pressure in thesecond part of the annulus forces the first and second legs radiallyapart to thereby maintain the first leg in sealing engagement with theinner tubular member and the fourth leg in sealing engagement with theouter tubular member; and wherein a pressure in the second part of theannulus greater than a pressure in the first part of the annulus forcesthe third and fourth legs radially apart to thereby maintain the firstleg in sealing engagement with the inner tubular member and the fourthleg in sealing engagement with the outer tubular member; whereby thefirst and second legs maintain sealing engagement with the inner andouter tubular members, respectively, whether the pressure in the firstpart of the annulus is greater than the pressure in the second part ofthe annulus or the pressure in the second part of the annulus is greaterthan the pressure in the first part of the annulus.
 17. The sealassembly of claim 16, wherein the first leg sealingly engages the innertubular member through at least a first sealing bump which is formed ona radially inner surface of the first leg and the fourth leg sealinglyengages the outer tubular member through at least a second sealing bumpwhich is formed on a radially outer surface of the fourth leg.
 18. Theseal assembly of claim 17, wherein the first and second sealing bumpsare located approximately in a first plane which is perpendicular to theaxial centerline of the inner and outer tubular members, the firstcavity comprises an axially inner end which is located approximately ina second plane that is parallel to the first plane and is spaced apartfrom the first plane in a direction toward the second part of theannulus, and the second cavity comprises an axially inner end which islocated approximately in a third plane that is parallel to the firstplane and is spaced apart from the first plane in a direction toward thefirst part of the annulus.
 19. The seal assembly of claim 16, furthercomprising first and second packoff members between which the first sealis positioned, the first packoff member being supported on at least oneof the inner and outer tubular members and the second packoff memberbeing movable toward the first packoff member to thereby mechanicallyenergize the first and fourth legs into sealing engagement with theinner and outer tubular members, respectively.
 20. The seal assembly ofclaim 19, wherein the first seal portion is formed integrally with thesecond packoff member.